In order to meet the requirements of Network Centric Warfare, existing sensing platforms, such as the E-2 early warning, command and control aircraft, will have to be leveraged through the use of emerging architectures and technologies. Specifically, they will be called upon to perform fast, accurate location of targets, including traditional threat emitters such as radars, which use waveforms that have widely separated pulses with well-defined leading edges. In addition, fast, accurate location of an emerging set of target emitters, which have more continuous waveforms, is becoming increasingly important. These non-traditional target emitters include communications terminals that might be associated with terrorists, drug dealers, urban combatants, and emergency-first-response rescue personnel. Such communications terminals may include cell phones, PDAs, laptop computers, and other devices.
To address these target emitters, legacy platforms will have to be equipped with the sensor and sensor-management capability, and the communications infrastructure to support multi-platform collaborative targeting. In a collaborative targeting system, participating sensor platforms can contribute multiple measurements that are dependant on the target emitter's location, such as the Angle of Arrival (AOA). By taking advantage of the geometries available with multiple platforms, the geometric dilution of precision (GDOP) resulting from finite measurement accuracy can be avoided, and fast yet accurate location can be obtained from measurements such as AOA.
Although AOA can generally be measured for most emitter types, other precision measurements, such as Time Difference of Arrival (TDOA), are traditionally applied to radar emitters, because radars emit easy-to-distinguish pulses with leading edges that enable time of arrival to be measured. Applying techniques to continuous waveform emitters, such as communications terminals, is less straightforward, however, due to the absence of a well-defined event, such as the leading edge of a pulse that would enable measurement of the time of arrival. There is a need, then, for a method for passively determining the location of continuous wave emitters in multi-platform network centric systems.